Deflocculating means for use in a paper making machine

ABSTRACT

A deflocculating mechanism for use in a paper making machine includes a support member such as a forming board or a foil blade for location beneath a forming fabric belt. The support member has an upper surface defining at least one groove that runs in a cross-machine direction, the groove being provided with retention device for holding an insert in a sliding engagement in the groove to induce micro-turbulence in pulp stock being carried by the forming fabric belt. A pressure pulse commences in the pulp stock from a single source at one side of the forming fabric as it passes over the leading edge of the insert and then travels across the fabric along the line of the insert as a single wave. This produces a more controlled agitation and deflocculation of the pulp stock.

RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

FIELD OF THE INVENTION

The present invention relates to a deflocculating means for use in apaper making machine. In particular it relates to a means which can beused in conjunction with a forming board or foil blade to reduceflocculation and produce a controlled agitation of the pulp stock.

BACKGROUND OF THE INVENTION

In a paper making machine, pulp stock, which comprises a thin aqueoussuspension of fibers and fillers is ejected from a headbox on to thesurface of a moving endless screen belt called a forming fabric, whichis made of woven metal wires or plastic filaments. The forming fabricpasses over various fabric support devices to withdraw the water toleave a thin formation of matted fibers that is lifted off the fabricand subsequently treated, ultimately to produce a finished sheet ofpaper.

The quality of the finished paper depends to a large extent on theuniformity of the fibre suspension in the pulp stock being maintainedduring the dewatering process which occurs on the forming fabric. Thus,means are conventionally employed to create micro-turbulence in the pulpstock on the forming fabric to prevent the fibers in the pulp fromagglomerating and forming flocs.

Typical deflocculating means comprise forming boards or foil bladeswhich are located beneath the forming fabric to interrupt the drainageof water and cause the development of pressure pulses in the pulp stock.Such a forming board is described in British patent GB 2190932, whichdescribes a board with an upper surface comprising one or moretransverse slots. The depth of the or each slot can be varied by thelocation in the slot of a slat. A plurality of slats of varyingthickness is provided so that the depth of the slot in the board can beadjusted according to the thickness of the slat used. In this way, theforming board can be readily adapted to produce the requisite degree ofturbulence required.

The object of the present invention is to provide a deflocculating meansfor use in a paper making machine which provides an improvement in thetear strength of the resulting paper over the aforementionedconventional means described above.

BRIEF SUMMARY OF THE INVENTION

According to the present invention there is provided a deflocculatingmeans for use in a paper making machine comprising a support member forlocation beneath a forming fabric belt, the support member having anupper surface defining at least one groove that runs in a cross-machinedirection, the groove being provided with retention means for holding aninsert in a sliding engagement in the groove in order to inducemicro-turbulence in pulp stock being carried by the forming fabric belt,and characterized in that the groove has a longitudinal axis which isangled at between 0.38° and 0.77° to a transverse axis in thecross-machine direction.

It has been found that a slight angling of the groove and thereby of theinsert to the transverse axis across the direction of travel of theforming fabric induces sideways moving pressure pulses in the pulp stockwhich results in a more controlled agitation of the pulp stock thaninserts which are simply mounted parallel to the transverse axis in aconventional fashion. In the latter case, the pulses produced are morechaotic because a multiplicity of waves are formed which tend tointerfere with one another, thus nullifying their effect in regions ofthe pulp stock. In the present invention, however, the pressure pulsecommences in the pulp stock from a single source at one side of theforming fabric as it passes over the leading edge of the insert and thentravels across the fabric along the line of the insert as a single wave.The agitation thus produced is therefore more uniform in nature andaffects the whole of the pulp stock equally.

Also, in a conventional arrangement, repeated agitation of the pulpstock tends to make the fibers therein align with the direction ofmovement of the forming fabric rather than retaining a random alignment,which is preferably if the resulting paper is to have a high tearstrength. The present invention, however, tends to realign the fibers sothat they are no longer parallel to their direction of travel on theforming fabric.

Preferably, the upper surface of the support member defines a pluralityof grooves running in a cross-machine direction.

The grooves may run parallel to one another across the surface butalternatively they can be arranged so that leading ends of the grooveswith respect to the direction of travel of the belt are located onopposite sides of the support surface.

Preferably also, the insert changes the depth of the groove.Alternatively, the insert may project above the level of the supportsurface so that if a plurality of grooves are arranged adjacent oneanother across the support surface, the inserts define a series ofcross-machine channels therebetween.

Preferably also, the upper surface of the insert is flat.

Preferably also, the upper surface of the insert has a downstreamportion which diverges backwards at an angle between 0° and 5°.

Preferably also, the trailing side walls of the grooves are angled sothat they slope in the direction of travel of the belt at an angle whichdiverges by up to 45° from the vertical.

Preferably also, the leading edge of the support member divergesdownwardly from the support surface at an angle of 30°.

Preferably also, the retaining means is provided by the groove defininga T-shaped or dovetail-shaped transverse cross-sectional profile intowhich a complementary shaped insert can be slidingly engaged from oneend of the groove.

The support member may comprise a forming board. Alternatively, it maycomprise a foil blade.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention will now be described by way of example withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view from one side of a forming board accordingto the present invention;

FIG. 2 is a side elevation of a insert for use in conjunction with theforming board shown in FIG. 2;

FIG. 3 is a plan view of the board shown in FIG. 1 but to a reducedscale; and

FIG. 4 is a side elevation of the board shown in FIG. 3 with threedifferent inserts located therein.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings, a forming board 1 comprisessubstantially flat, rectangular upper support surface 3 and a lowersurface 3. Each of the surfaces 2 and 3 defines a series of grooves 4and 5 respectively. The board 1 is also provided with a leading edge 6and a trailing edge 7, with respect of the direction of travel B of aforming fabric belt beneath which it is to be located in a paper makingmachine. As is conventional, the leading edge 6 of the board 1 divergesdownwardly from the upper surface 2 at an angle a of around 30°.

Both sets of grooves 4 and 5 are open ended and run across the board 1in a cross-machine direction with regard to the direction of travel B ofthe forming fabric. The cross-sectional profiles of the grooves 5 in thelower surface are T-shaped uniformly along the length of the groove toenable the board 1 to be attached in a conventional fashion to T-shapedcross-rails mounted on a frame located beneath the forming fabric belt.

The grooves 4 in the upper surface 2 of the board 1 also have a uniformT-shaped transverse cross-sectional profile to provide a retaining meansfor an insert 8 in the form of a complementarily shaped slat that can beslidingly engaged in the groove 4 from one end thereof. However, thegrooves 4 need not have a T-shaped profile, other profiles also beingsuitable to provide the retaining means, for example a dovetail-shapedprofile.

Whereas the grooves 5 in the lower surface 3 of the board run 1transversely across the board normal to the direction of travel B of theforming fabric belt, the grooves 4 in the upper surface 2 have alongitudinal axis which is angled at between 0.38° and 0.77° to atransverse axis in the cross-machine direction. In practice, formingboards 1 have a width which varies between 2000 mm and 11000 mm, thismeans that there will be an approximate variation of between 13 mm and148 mm between the distance of the leading end 9 of the leading edge 10of the groove 4 from the leading edge 6 of the board 1 and the distanceof the trailing end 11 of the leading edge 10 of the groove 4 from theleading edge 6 of the board 1. This variation is indicated in FIG. 3 byshowing the distance x between the leading edge 6 of the board and theleading end 9 of the leading edge 10 of the groove 4 closest to theleading edge 6, and the distance x+y between the leading edge 6 and thetrailing end 11 of the edge 10, y being approximately between 13 mm and148 mm in length.

Although in the drawings three grooves 4 are shown in the forming board1 which are all arranged parallel to one another, the grooves 4 need notbe arranged in this fashion. Also, the numbers of grooves 4 in the board1 can be varied as required. In some applications of the invention itwill be advantageous to arrange the grooves 4 so that the leading ends 9of the grooves 4 with respect to the direction of travel B of the beltare located on opposite sides of the support surface 3. In this case,therefore, the grooves 4 will lie at oblique angles to one anotheracross support surface 2 of the board 1. In particular, the adjacentgrooves 4 of a series can be arranged to run obliquely to one another.

The inserts 8 provided for sliding engagement in the grooves 4 mayeither change the depth of the groove 4 by being of a smaller depth thanthe depth of the groove 4 or may project above the level of the supportsurface 2. In the latter case, if a plurality of parallel grooves 4 arearranged adjacent one another across the support surface, the inserts 8will define a series of cross-machine channels therebetween. It will beappreciated that in essence this will produce the same effect as the useof the inserts 8 in the former case where the grooves 4 themselvesdefine the cross-machine channels.

In addition to the aforementioned inserts, inserts 8 may also beprovided which are the same depth as the depth of the grooves 4,effectively to blank out any grooves 4 in the board 1 which may not berequired for a particular application.

The upper surface of the inserts 8 is preferably smooth and flat.However, some inserts 8, such as the insert shown in FIG. 2 may have anupper surface 12 that has a downstream portion 13 which divergesbackwards at an angle b between 0° and 5°. Also, the trailing edges 14of the grooves 4 may angled so that they slope in the direction oftravel of the belt at an angle which diverges by up to 45° from thevertical, as shown in FIG. 1. These features assist in the production ofthe micro-turbulence in the pulp stock by forcing any water which hasdrained through the forming fabric as a result of the action of theinsert 8 to be washed back gently through the fabric into the pulp stockto deflocculate the fibers.

In use, as previously mentioned, the forming board 1 is mountedconventionally beneath a forming fabric belt in a paper making machine.As the belt passes over the board 1, the cross-machine channels definedby the board 1 by the combination of the grooves 4 and inserts 8 inducepressure pulses in the pulp stock. This occurs principally by forcingwater which has draining from the stock through the forming fabric backthrough the fabric into the pulp. In the present invention, thecross-machine channels will be encountered first at their leading ends 9at one side of the fabric. These will set up a pressure pulse in thepulp stock that will move sideways across the fabric as fabric passesover the grooves 4. Hence, a single wave is formed which travels acrossthe fabric along the line of the insert 8 and this produces a controlledagitation of the pulp stock. Also, the sideways traveling wave willagitate the fibers and induce them to move out of alignment with thedirection of travel B on the forming fabric, which would otherwise tendto be their preferred direction of alignment.

A forming board 1 as described above may be made from any suitablematerial, which is easy to machine and will withstand wear. Particularlysuitable for the purpose are machinable plastics materials, such as highdensity polyethylene, as they will not be corroded by the water drainingout from the pulp stock.

As previously stated, both forming boards and foil blades can be adaptedin accordance with the present invention. Whilst a forming board hasbeen used in the example given above to demonstrate the invention, a manskilled in the art will appreciate that a foil blade in accordance withthe invention could be readily manufactured.

1. A deflocculating means for use in a paper making machine comprises: asupport member located beneath a forming fabric belt, the support memberhaving an upper surface defining at least one groove that runs in across-machine direction, the groove being comprised of a retention meansfor holding an insert in a sliding engagement in the groove in order toinduce micro-turbulence in pulp stock being carried by the formingfabric belt, wherein the groove has a longitudinal axis which is angledat between 0.38° and 0.77° to a transverse axis in the cross-machinedirection.
 2. A deflocculating means as claimed in claim 1, wherein anupper surface of the support member defines a plurality of groovesrunning in a cross-machine direction.
 3. A deflocculating means asclaimed in claim 1, wherein said grooves run parallel to one anotheracross the surface of said support member.
 4. A deflocculating means asclaimed in claim 1, wherein said grooves are arranged so that leadingends of the grooves with respect to the direction of travel of the beltare located on opposite sides of the support surface.
 5. Adeflocculating means as claimed in claim 1, wherein the insert changesthe depth of the groove.
 6. A deflocculating means as claimed in claim1, wherein the insert projects above the level of the support surface sothat if a plurality of grooves are arranged adjacent to one anotheracross the support surface, the inserts define a series of cross-machinechannels therebetween.
 7. A deflocculating means as claimed in claim 1,wherein the upper surface of the insert is flat.
 8. A deflocculatingmeans as claimed in claim 1, wherein the upper surface of the insert hasa downstream portion which diverges backwards at an angle between 0° and5°.
 9. A deflocculating means as claimed in claim 1, wherein trailingside walls of the grooves are angled so that they slope in the directionof travel of the belt at an angle which diverges by up to 45° from thevertical.
 10. A deflocculating means as claimed in claim 1, wherein aleading edge of the support member diverges downwardly from the supportsurface at an angle of 30°.
 11. A deflocculating means as claimed inclaim 1, wherein the retaining means is provided by the groove defininga T-shaped or dovetail-shaped transverse cross-sectional profile intowhich a complementary shaped insert can be slidingly engaged from oneend of the groove.
 12. A deflocculating means as claimed in claim 1,wherein said support member comprises either a forming board or a foilblade.